Linear traveling wave tube amplifier utilizing input drive limiter for optimization

• US 6,369,648 B1
• Filed: 04/21/1999
• Issued: 04/09/2002
• Est. Priority Date: 04/21/1999
• Status: Expired due to Term

• Current Assignee: Hughes Electronics Corporation (AT&T, Inc.)
• Original Assignee: Hughes Electronics Corporation (AT&T, Inc.)
• Inventors: Kirkman, George F.
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Choe, Henry
• Application Number:
  US09/295,720
• Time in Patent Office: 1,084 Days
• Field of Search: 330/43, 330/140, 330/141, 330/281, 330/284, 330/149
• US Class Current: 330/43
• CPC Class Codes: H03F 1/0205 in transistor amplifiers
• CPC Class Codes: H03F 3/58 using travelling-wave tubes
• CPC Class Codes: H03G 7/002 in untuned or low-frequency amplifiers, e.g. audio amplifiers H03G7/007, H03G7/001, H03G7/008, H03G7/02, H03G7/06 take precedence

Abstract

A linearized traveling wave tube amplifier with average power limiter is disclosed. The device includes an average power limiter for the purpose of preventing a TWT from operating at output powers higher than the required operating point. The device includes a detector for dynamically producing a detector signal proportional to an average power of an input signal and substantially independent from a peak power of the input signal, and an attenuator, in communication with the detector and the amplifier, for dynamically attenuating the input signal according to the detector signal. The limiter allows the TWTs to be optimized for performance at the required operating point, resulting in higher efficiency, and eliminates the need to size the amplifier for a power level any larger than the required operating point which reduces the cost and complexity of the system. The limiter protects the TWT while not degrading the linear performance of the TWT by limiting the average power while allowing peak powers of short duration to pass with low loss.

Claims

1. An traveling wave tube amplifier system, comprising:

a traveling wave tube amplifier;

a detector for dynamically producing a detector signal proportional to an average power of an input signal and substantially independent from a peak power of the input signal; and

an attenuator in communication with the detector and said traveling wave tube amplifier, for dynamically attenuating the input signal according to the detector signal.

2. The device of claim 1, wherein said current rectifier further comprises a low pass filter series coupled to the cathode of said diode.

3. The device of claim 2, wherein the low pass filter produces a low pass filter output signal lagging a low pass filter input signal according to a first order time constant.

4. The device of claim 2, wherein the low pass filter produces a low pass filter output signal lagging a low pass filter input signal according to a multiple order time constant.

5. The device of claim 2, wherein the low pass filter comprises at least one resistive element coupled in parallel with at least one capacitive element.

6. The device of claim 5, wherein a resistance of the resistive element and the capacitance of the capacitive element are selected so as to substantially limit a detector response time to greater than 10 microseconds.

7. The device of claim 1, wherein the shunt limiter comprises a field effect transistor (FET) having a gate in communication with the detector signal and a source in communication with the ground.

8. The device of claim 1, wherein the FET is an enhancement FET.

9. The device of claim 1, wherein the shunt limiter is in communication with the detector signal via a signal conditioner, the signal conditioner implementing a gain relationship between the detector signal and the shunt limiter, wherein the gain relationship is selected to limit the average power output of the amplifier to a pre-selected value.

10. The device of claim 4 wherein the signal conditioner further implements an impedance relationship between the detector and the shunt limiter.

11. The device of claim 1, further comprising a predistortion linearizer coupled between the input signal and the detector for preconditioning the input signal.

12. A method of processing an input signal of a traveling wave tube amplifier, comprising the steps of:

dynamically determining a value proportional to an average power of the input signal and substantially independent from a peak power of the input signal of a traveling wave tube amplifier;

dynamically attenuating the input signal according to the value; and

applying the dynamically attenuated input signal to a traveling wave tube amplifier to produce an output signal.

13. The method of claim 12, wherein the amplifier is a traveling wave tube amplifier.

14. The method of claim 13, wherein the step of determining a value proportional to the average power of the input signal and substantially independent from the peak power of the input signal comprises the steps of:

rectifying the input signal; and

low-pass filtering the rectified input signal.

15. The method of claim 14, wherein the step of rectifying the output signal comprises the step of passing the signal through a diode.

16. The method of claim 15, wherein the step of low pass filtering the rectified input signal comprises the step of passing the rectified amplifier signal through a low pass filter comprising a capacitive element coupled in parallel with a resistive element.

17. The method of claim 14, wherein the step of low pass filtering the rectified input signal comprises the step of producing a detector output signal lagging the input signal according to a first order time constant.

18. The method of claim 17, wherein the first order time constant is chosen to prevent damage to the amplifier.

19. The method of claim 18, wherein the first order time constant is between 10 microseconds and 1 millisecond.

20. The method of claim 14, wherein the step of low pass filtering the rectified input signal comprises the step of producing a detector output signal lagging the input signal according to a multiple order time constant.

21. The method of claim 12, wherein the step of shunting the input signal according to the rectified and low pass filtered input signal comprises the step of applying the rectified and low pass filtered input signal to a gate of a field effect transistor (FET).

22. The method of claim 14, further comprising the step of predistortion linearizing the input signal.

23. A signal embodied in a carrier wave in an output signal of a traveling wave tube amplifier, the signal produced by performing the method steps of:

dynamically determining a value proportional to an average power of an input signal of a traveling wave amplifier and substantially independent form a peak power of the input signal;

dynamically attenuating the input signal according to the value; and

applying the dynamically attenuated input signal to a traveling wave tube amplifier to produce an output signal.

24. The signal of claim 23, wherein the amplifier is a traveling wave tube amplifier.

25. The signal of claim 24, wherein the method step of determining a value proportional to the average power of the input signal and substantially independent from the peak power of the input signal comprises the method steps of:

rectifying the input signal; and

low-pass filtering the rectified input signal.

26. The signal of claim 25, wherein the method step of rectifying the amplifier output signal comprises the method step of passing the input signal through a diode.

27. The signal of claim 26, wherein the method step of low pass filtering the rectified amplifier signal comprises the method step of passing the rectified amplifier signal through a low pass filter comprising a capacitive element coupled in parallel with a resistive element.

28. The signal of claim 25, wherein the method step of low pass filtering the rectified input signal comprises the method step of producing a detector output signal lagging the input signal according to a first order time constant.

29. The signal of claim 25, wherein the first order time constant is chosen to prevent damage to the amplifier.

30. The signal of claim 29, wherein the first order time constant is between 10 microsecond and 1 millisecond.

31. The signal of claim 25, wherein the method step of low pass filtering the rectified input signal comprises the method step of producing a detector output signal lagging the input signal according to a multiple order time constant.

32. The signal of claim 23, wherein the method step of shunting the input signal according to the rectified and low pass filtered input signal comprises the method step of applying the rectified and low pass filtered input signal to a gate of a field effect transistor (FET).

33. The signal of claim 25, wherein the method steps further comprise the step of predistortion linearizing the input signal.